Hibernate高级实体关联映射之多值的实体关联(一对多关联,使用bag)

包(bag)有着可以用于一对多实体关联的所有集合的最有效的性能特征。默认情况下，hibernate中的集合只有当它们在应用程序中第一次被访问进才被加载。因为bag不必维持其元素的索引，或者检查重复元素，可以添加新元素给bag,而不触发加载。如果要映射一个可能很大的实体引用的集合，这就是一项重要的特性。

一般来说，对于一对多的关联，我们认为bag是它最好的反向集合。为了把一对多关联映射为bag,必须用Collection和ArrayList。

pom.xml:

]<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion>
<groupId>hibernateTest</groupId>
<artifactId>hibernateTest</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>jar</packaging>
<name>hibernateTest</name>
<url>http://maven.apache.org</url>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>3.3.1.GA</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-nop</artifactId>
<version>1.5.2</version>
</dependency>
<dependency>
<groupId>javassist</groupId>
<artifactId>javassist</artifactId>
<version>3.4.GA</version>
</dependency>
<dependency>
<groupId>c3p0</groupId>
<artifactId>c3p0</artifactId>
<version>0.9.1</version>
</dependency>
<dependency>
<groupId>com.oracle</groupId>
<artifactId>ojdbc14</artifactId>
<version>10.2.0.3.0</version>
<scope>runtime</scope>
</dependency>
</dependencies>
<build>
<finalName>hibernateTest</finalName>
<resources>
<resource>
<directory>src/main/resources</directory>
</resource>
<resource>
<directory>src/main/java</directory>
<excludes>
<exclude>**/*.java</exclude>
</excludes>
</resource>
</resources>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.6</source>
<target>1.6</target>
<encoding>UTF-8</encoding>
</configuration>
</plugin>
</plugins>
</build>
</project>

resources/hibernate.cfg.xml:

]<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-configuration
PUBLIC "-//Hibernate/Hibernate Configuration DTD//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory name="sessionFactory">
<!-- 指定连接数据库所用的驱动 -->
<property name="hibernate.connection.driver_class">oracle.jdbc.driver.OracleDriver</property>
<!-- 指定连接数据库的url，hibernate连接的数据库名 -->
<property name="hibernate.connection.url">jdbc:oracle:thin:@localhost:1521:XE</property>
<property name="hibernate.connection.useUnicode">true</property>
<property name="hibernate.connection.characterEncoding">gbk</property>
<!-- 指定连接数据库的用户名 -->
<property name="hibernate.connection.username">system</property>
<!-- 指定连接数据库的密码 -->
<property name="hibernate.connection.password">password</property>
<!-- 指定连接池里最大连接数 -->
<property name="hibernate.c3p0.max_size">20</property>
<!-- 指定连接池里最小连接数 -->
<property name="hibernate.c3p0.min_size">5</property>
<!-- 指定连接池里连接的超时时长,以秒为单位 -->
<property name="hibernate.c3p0.timeout">120</property>
<!-- 指定连接池里最大缓存多少个Statement对象 -->
<property name="hibernate.c3p0.max_statements">100</property>
<!-- 每隔XX秒检查连接池里的空闲连接 ，单位是秒 -->
<property name="hibernate.c3p0.idle_test_period">120</property>
<!-- 当连接池里面的连接用完的时候，C3P0一次获取的新的连接数 -->
<property name="hibernate.c3p0.acquire_increment">2</property>
<!-- 指定数据库方言 -->
<property name="dialect">org.hibernate.dialect.OracleDialect</property>
<!-- 显示Hibernate持久化操作所生成的SQL -->
<property name="show_sql">true</property>
<!-- 将SQL脚本进行格式化后再输出 -->
<property name="hibernate.format_sql">true</property>
<!-- 罗列所有的映射文件 -->
<mapping resource="pojo/User.hbm.xml" />
<mapping resource="pojo/Address.hbm.xml" />
</session-factory>
</hibernate-configuration>

pojo/User.java:

]package pojo;
import java.util.ArrayList;
import java.util.Collection;
public class User {
private String id;
private String userName;
private String password;
private String email;
//使用bag映射
private Collection<Address> addressList = new ArrayList<Address>();

public String getId() {
return id;
}
@SuppressWarnings("unused")
private void setId(String id) {
this.id = id;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public Collection<Address> getAddressList() {
return addressList;
}
public void setAddressList(Collection<Address> addressList) {
this.addressList = addressList;
}
//双向关联
public void addAddress(Address address){
this.addressList.add(address);
address.setUser(this);
}
}

pojo/User.hbm.xml:

]<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="pojo">
<class name="User" table="MYUSER" dynamic-insert="true" dynamic-update="true">
<id name="id" column="ID" type="string">
<generator class="uuid.hex" />
</id>
<property name="userName" column="USERNAME" type="string"/>
<property name="password" column="PASSWORD" type="string"/>
<property name="email" column="EMAIL" type="string"/>
<!-- 注意这里 -->
<bag name="addressList" inverse="true" cascade="save-update">
<key column="USER_ID"/>
<one-to-many class="Address"/>
</bag>
</class>
</hibernate-mapping>

pojo/Address.java:

]package pojo;
public class Address {
private String id;
private String street;
private String zipCode;
private String city;
private User user;

public String getId() {
return id;
}
@SuppressWarnings("unused")
private void setId(String id) {
this.id = id;
}
public String getStreet() {
return street;
}
public void setStreet(String street) {
this.street = street;
}
public String getZipCode() {
return zipCode;
}
public void setZipCode(String zipCode) {
this.zipCode = zipCode;
}
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
}

pojo/Address.hbm.xml:

]<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="pojo">
<class name="Address" table="ADDRESS" dynamic-insert="true" dynamic-update="true">
<id name="id" column="ID" type="string">
<generator class="uuid.hex" />
</id>
<property name="street" column="STREET" type="string"/>
<property name="zipCode" column="ZIPCODE" type="string"/>
<property name="city" column="CITY" type="string"/>
<!-- 注意这里 -->
<many-to-one name="user" column="USER_ID" class="User" not-null="true"/>
</class>
</hibernate-mapping>

util/HibernateUtil.java:

]package util;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class HibernateUtil {
private static SessionFactory sessionFactory;
static{
try {
sessionFactory = new Configuration().configure().buildSessionFactory();
} catch (Throwable e) {
throw new ExceptionInInitializerError(e);
}
}
public static SessionFactory getSessionFactory(){
return sessionFactory;
}
public static void shutdown(){
getSessionFactory().close();
}
}

util/Manager.java:

]package util;
import org.hibernate.Session;
import org.hibernate.Transaction;
import pojo.Address;
import pojo.User;

public class Manager {
public static void main(String[] args) {

Address address = new Address();
address.setCity("guangzhou");
address.setStreet("北京路");
address.setZipCode("510000");

User user = new User();
user.setUserName("fhd");
user.setPassword("000000");
user.setEmail("8888@163.com");
user.addAddress(address);

Session session = HibernateUtil.getSessionFactory().openSession();
Transaction transaction = session.beginTransaction();

session.save(user);

transaction.commit();
session.close();
}
}

表结构：

]MYUSER表:
ID,
USERNAME,
PASSWORD,
EMAIL
ADDRESS表：
ID,
STREET,
ZIPCODE,
CITY,
USER_ID

输出sql:

]Hibernate:
insert
into
MYUSER
(USERNAME, PASSWORD, EMAIL, ID)
values
(?, ?, ?, ?)
Hibernate:
insert
into
ADDRESS
(STREET, ZIPCODE, CITY, USER_ID, ID)
values
(?, ?, ?, ?, ?)